You can use any of the Olympus Guns (except FL-40) select TTL-AUTO and away you go.

The RC guns can even be used Off Camera to avoid all the usual horrors of on camera flash.

One good technique is to get a manual metering of the background, set the camera to how you want that to look and then let the flash adjust itself via preflash to provide light to the foreground subjects.

Flash is something that needs to be experimented with and notes taken to remember what works for how you want the end result.

Best tip is to use minimum light from the gun as possible and diffuse it as much as you can.